1. Field of the Invention
The present invention relates to copying apparatus wherein the document glass plate or the optical scanning system is returned to the starting position before the start of copying.
2. Description of the Prior Art
As a copying apparatus, various types are known such as a mechanical optical one wherein exposure scanning is made while the light is applied to the original to be copied and the reflected light from the original is projected directly on the photosensitive member that is evenly charged, and thus an electrostatic latent image is formed on the photosensitive member; or an electro-optical one wherein an electric discharge is made between a dielectric and a means such as a multistylus electrode to be used after the reflected light from the original is converted to electrical image signals with the use of a solid state image sensor, and thus an electrostatic latent image is formed on the photosensitive member or on the dielectric member. In any one of them, an exposure scanning means namely a document glass plate or an optical scanning system (hereinafter called "a platen or the like") reciprocates in order to scan the original. A platen or the like, using a driving source, makes a forward movement through a forward clutch (a first driving means) and a backward movement by a reverse clutch (a second driving means), and is positioned at a fixed starting position before the start of the forward movement or after the completion of the backward movement.
The exposure action of such a platen or the like will be described with the reference of FIG. 1.
FIG. 1 shows a schematic view of a known copying apparatus. The top of the main frame 1 supports platen 2 on which the original M is placed. Optical scanning system 4 is arranged so that it reciprocates on the guide rod 3 extending horizontally within the main frame 1 and beneath platen 2. The optical scanning system 4 consists of a first movable stand 41 on the top of which the exposure lamp 41a for the original is fixed and inside of which the mirror 41b and the lens 41c are arranged, a secondary movable stand 42 on which the mirrors 42a and 42b are arranged and a mirror 43 attached to a part of the camera obscura 5. At the center in the main frame 1, the photosensitive member drum 6 is mounted for rotation in the direction of the arrow near the circumferential surface thereof, a charge generator 7, a developing device 8, a transfer electrode 9, a separation electrode 10, a change eliminating electrode 11 and cleaning device 12 are arranged successively. At the right side in the main frame 1, paper feeding device 13 is arranged and in this particular example, two types of recording paper in different sizes are loaded in the paper feeding cassettes 13a and 13b respectively and are set in the main frame 1. The numeral 13c indicates paper feeding rollers that feeds the recording paper loaded in the paper feeding cassettes up to the standby position A, and 13d are a pair of secondary paper registration rollers that convey the recording paper to the transfer position. The numeral 14 is a conveyance unit that conveys the recording paper after transfer to the fixing unit 15. The fixing unit 15 consists of a heater pressure roller 15a and a paper ejecting roller 15b. The numeral 16 is a paper receiving tray.
In the copying apparatus with the aforesaid structure, the microswitch MS1 for detecting the starting position and the microswitch MS2 located at a distance from MS1 for starting the paper registration rollers 13d are arranged near the left end of the guide rod 3 of the optical scanning system 4. At the input side of the paper registrating rollers 13d, a microswitch MS3 for detecting the recording paper is arranged, and at the input side of the paper ejecting roller 15b, the microswitch MS4 for detecting the exit of the recording paper is arranged. A shock-absorbing spring 17 is arranged around the guide rod 3 at the side of the first movable stand 41 on the second movable stand 42.
Before the start of recording operation, the optical scanning system 4 will be positioned at the starting position (the extreme left position on FIG. 1) and the microswitch MS1 for detecting the on start position is in the state. If, under such condition, the recording button SW (FIG. 2) is pressed, the main drive motor M1 starts rotating and after the microswitch MS1 is confirmed to be in the state of ON, a forward clutch CL1 (not illustrated) is energized to drive the optical scanning system 4 and the optical scanning system 4 is driven along the guide rod 3 and thus the scanning of an original is started. In the case that the microswitch MS1 is not in the ON state when the recording button is pressed, namely if the optical scanning system 4 is not in the start position, the reverse clutch CL2 (not illustrated) is energized and the optical scanning system 4 is returned to its start position, the microswitch MS1 is turned on and the reverse clutch is neutralized and the forward clutch is energized. Concurrently with the start of the forward movement of the optical scanning system 4, the recording paper is fed by the paper feeding roller 13c. With the microswitch MS3 is turned on, the paper feeding roller 13c is neutralized and the paper enters the state of standby at the position A where the paper hits the paper registration roller 13d. When the microswitch MS2 is turned on after certain period of time from the start of the movement of the optical scanning system 4, the paper registration rollers 13d are driven and the recording paper that has been in the state of standby is fed again toward the transfer position B. By doing like this, it is possible to make the leading edge of the recording paper coincide with the leading edge of the electrostatic latent image of the original formed on the photosensitive member drum 6 by the scanning of the original made by the optical scanning system 4. Thus, the optical scanning system 4 scans the original while it advances and the reflected light from the original is projected onto the photosensitive member drum 6 causing the formation of the electrostatic latent image of the original. On the other hand, the recording paper itself continues to be fed by the paper registration rollers 13d. later when microswitch MS3 is turned off after the trailing edge of the recording paper has passed completely by, the forward clutch that has been driving the optical scanning system 4 up to that time is deenergized and the reverse clutch is energized. At this moment, the optical scanning system 4 has completed the scanning of the original.
After movement of aforesaid optical scanning system, the optical scanning system 4 starts returning at higher speed than that of forward movement, and when the microswitch MS1 for detecting the start position is actuated, the reverse clutch is neutralized and the optical scanning system stops, compressing the shock-absorbing spring 17 that is a shock-absorbing means arranged around the guide rod 3, and it is possible that the optical scanning system 4 does not stop precisely at the start position due to the compression force of spring 17. If the optical scanning system 4 does not stop precisely at the start position, there arises the problem that the formation of an image will be started on the drum 6 before the illumination lamp or the like reaches its sufficient brightness in the next recording cycle because the optical scanning system will start from a position that is different from the regular start position. So, for the solution of this problem, the start position of the platen can be set at a position that is far behind the scanning zone, which, however, makes the total apparatus bulky. So, as a solution to solve this problem without making the total apparatus bulky considering the recent tendency toward compactness, there has been known a method wherein the reverse clutch is operated temporarily before the next recording cycle and the platen and the like are forcibly returned to the regular start position. In the case the platen and the like stop at the position far away from the regular position, if they are forcibly returned, they easily return to the regular start position due to the inertia of the platen and the like but in case they stop at a position slightly away from the regular start position, if they are attempted to be returned under force, they need a greater force than that of the case in which they stop at the position far away from the regular start position because of the strong reaction caused by the compression force of the spring; and the reverse clutch slips and slipping is generated between the pulley that transmits the power to the reverse clutch and the wire and thus the platen and the like sometimes do not return to the regular start position.